That might be news to both car buyers and the entire rest of the auto industry, all of whom take the IIHS tests very seriously.

The most recent IIHS tests were performed on six large sedans, three of which qualified for the IIHS's highest award of Top Safety Pick+, a highly desirable and much-researched designation.

Those cars were the latest versions of the Lincoln Continental, the Mercedes-Benz E-Class, and the Toyota Avalon.

The Tesla Model S, along with the Chevrolet Impala and the Ford Taurus, did not receive the designation because they earned only an "Acceptable" rating, rather than the top score of "Good," on the IIHS small-overlap frontal-crash test.

That's not surprising: that tough new test was added only in 2012. By that time, the designs for all three sedans had been finalized.

While a few makers' cars, notably those from Volvo, tend to do well in any new tests, most makers "design to the tests" to a greater or lesser degree—meaning those older cars' structures weren't designed to pass a test the makers didn't know about.

The IIHS spent considerable time in its release discussing the results it achieved for Tesla's highest-production vehicle.

It noted that the Model S was initially rated Acceptable when first tested for small overlap, a new test it had added to show how a vehicle behaves if only the driver's front corner hits another vehicle, a pole, or a tree.

The problem in that first test had been excess forward movement of the crash-test dummy's torso, which let the dummy's head hit the steering wheel even though it was cushioned by an airbag in between.

In Tesla Model S electric cars built after January 2017, the company had changed the seat belt in an attempt to reduce such forward movement—but when the institute tested an updated Model S, the problem recurred. Hence, the rating wasn't changed.

The IIHS noted that the original and updated Model Ses tested had identical structures, but the test of the newer car actually produced a greater intrusion into the driver's compartment because the displacement of the left-front wheel in the crash was inconsistent.

Maximum intrusion increased from less than 2 inches to 11 inches in the lower part and to 5 inches at the instrument panel in the second test.

The first test produced a top rating of Good for structural integrity, the institute wrote, while the test of the updated car earned it only an Acceptable rating.

But the IIHS combined those two structural ratings—which led to an Acceptable result for both the structural-integrity and overall Model S ratings.

The left-front corner of the battery case under the passenger compartment was also damaged by the greater deformation found in the second test, though the IIHS noted that damage was in an area without lithium-ion cells, so it didn't affect the ultimate rating.

However, versions of the Model S with higher-capacity batteries may have cells in that area, although Tesla told the institute that the structure of the battery pack differs as well—so those versions (presumably those with 100-kilowatt-hour batteries) are specifically not covered by this rating.

The agency also noted:

The Model S is only available with headlights that earn a poor rating and hasn't been rated yet for front crash prevention. While automatic braking comes standard, the software for the feature was only recently activated.

The IIHS released its results at midnight Eastern time this morning, and the company has already responded to the results—denigrating the relative value of the IIHS tests and suggesting that the institute had "its own subjective purposes."

Those purposes, as seems relatively clear by the group's long history, is to urge the industry to build safer cars that are more capable of avoiding crashes, and reduce occupant injuries and deaths when crashes do occur.

In a statement e-mailed to Business Insider and reprinted in that outlet's coverage of the IIHS crash-test results for the Model S, Tesla wrote:

While IIHS and dozens of other private industry groups around the world have methods and motivations that suit their own subjective purposes, the most objective and accurate independent testing of vehicle safety is currently done by the U.S. Government which found Model S and Model X to be the two cars with the lowest probability of injury of any cars that it has ever tested, making them the safest cars in history.

The NHTSA, the federal agency to which Tesla refers, gave the rear-wheel-drive 2013 Tesla Model S its top rating of five stars in overall safety, frontal crash, side crash, and rollover protection.

That rating continued for 2014, but for 2015, the agency did not give an overall or frontal-crash rating to all-wheel-drive versions of the Model S.

It continued to give five-star ratings to one "early release" rear-wheel-drive Model S for 2016, but the "later release" Model S versions (which IIHS refers to) for 2016, as well as all 2017 Model S versions, remain unrated by the NHTSA.

We've reached out to Tesla for comment, and will update this story if we receive new information.